Salt separator and a method for producing a methane-containing gas mixture from biomass using a salt separator

Abstract

A salt separator separates salts and/or solid materials from a pumpable aqueous fluid mixture under process conditions, which lie in the range of the critical point for the fluid mixture. The salt separator contains a reaction zone in a cavity for transforming the pumpable aqueous fluid mixture into a raw mixture, e.g. a methanation reaction, and a feed opening for the pumpable aqueous fluid mixture to the cavity. The feed opening is realized in a rising pipe that protrudes into the cavity. A first extraction opening is provided for the raw mixture freed of salts and/or solid materials. The first extraction opening is arranged in the upper region of the cavity and a second extraction opening is provided for a brine containing the salt and/or the solid materials. The second extraction opening is arranged in the lower region of the cavity and is located lower down than the feed opening.

Claims

1. A combination, comprising: a salt separator for separating at least one of salts or solid materials from a pumpable aqueous fluid mixture under process conditions; and a catalytic converter configured for performing a methanation reaction; the salt separator including: a case with walls defining a reaction zone in a form of a cavity for transforming the pumpable aqueous fluid mixture into a raw mixture for further processing, said case having a bottom; a rising pipe having a feed opening for feeding the pumpable aqueous fluid mixture to said cavity, said rising pipe protruding through said bottom of said case and into said cavity such that said feed opening is displaced away from said bottom of said case; said cavity having an upper region with a first extraction opening formed therein for the raw mixture, wherein the raw mixture at said first extraction opening has been freed from at least one of the salts or the solid materials, said first extraction opening configured for supplying the raw mixture, which has been freed from at least one of the salts or the solid materials, to said catalytic converter; and said cavity having a lower region with a second extraction opening formed therein for a brine containing at least one of the salts or the solid materials, said second extraction opening is disposed lower down than said feed opening.

2. The combination according to claim 1, wherein said cavity is cylindrical and is vertically aligned, and said cavity has a diameter and a vertical length that is greater than said diameter.

3. The combination according to claim 1, wherein said first extraction opening is disposed in a region of a highest point of said cavity.

4. The combination according to claim 1, wherein said second extraction opening is disposed in a region of a lowest point of said cavity.

5. The combination according to claim 1, wherein said feed opening is disposed at a cavity-sided end of said rising pipe which protrudes vertically into said cavity.

6. The combination according to claim 1, further comprising at least one heating element located on at least one of said walls of said case.

7. The combination according to claim 1, wherein the pumpable aqueous fluid mixture lies substantially in a range of a critical point for the pumpable aqueous fluid mixture.

Description

BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWING

(1) Advantageous embodiments of the present invention are explained in more detail hereinafter with reference to the diagram for the salt separator and the method performed in exemplary fashion therewith for the gasification of biomass (e.g. wood or manure-solid materials). The figures show:

(2) FIG. 1 A diagrammatic view of a longitudinal section through a salt separator; and

(3) FIG. 2 A chronological sequence of the specific conductivity of a reactant of 10 wt % iso-propanol in water with a salt loading of 0.1 mol/l sodium sulfate and 0.05 mol/l potassium sulfate in a salt separator in accordance with FIG. 1 at a temperature of 450 C. and a pressure of 300 bar.

DESCRIPTION OF THE INVENTION

(4) FIG. 1 shows a diagrammatic view of a longitudinal section through a salt separator 2, as used for separating salts and/or solid materials from an aqueous fluid mixture. The raw product freed of salts and/or solid materials then undergoes further processing, e.g. a methanation reaction, wherein due to the eliminated salt and/or solid material content, a high level of selectivity and long service life of any catalytic converters 18 employed and a low level of corrosion of the surface subjected to the process can be achieved.

(5) The salt separator 2 typically comprises a stainless steel case 4 (or another suitable material such as titanium or a nickel alloy) which encloses a cylindrical cavity 6. In this sense, the cavity 6 is a reaction chamber in which salts dissolved in the aqueous fluid mixture can be extracted under the thermodynamic conditions prevailing in the cavity 6, which essentially correspond to the critical point for the fluid mixture. In the lower region of the cavity 6 a supply 8 is provided through which the aqueous fluid mixture is fed into the cavity 6 under high pressure of 200 to 400 bar at a temperature of approximately 350 to 500 C. In the process, the aqueous fluid mixture is released into the cavity 6 from a rising pipe 10. Essentially, at the highest position in the cavity 6 a first extraction opening 12 for a raw fluid largely freed of salts and/or solid materials which can then be introduced to the actual further processing, e.g. a methanation reaction, while achieving the aforementioned advantages. Essentially, at the lowest position in the cavity 6 a second extraction opening 16 for a brine comprising the salt and/or solid materials is provided which is thereby extracted from the further handling process. To maintain the high temperatures in the cavity 6, heating elements 14 in the form of resistance and/or induction heating elements arranged on the walls of the cavity are provided. However, alternatively or in addition, heating of the external wall by means of hot gases such as, for example, exhaust gases from firing or process off-gases, is also possible. Furthermore, it is possible to achieve the required heating by adding oxidizing agents to the entering fluid, e.g. nitrates, oxygen or hydrogen peroxide.

(6) It comes as a complete surprise that the introduction of the aqueous fluid mixture from below into the salt separator 2 had the pleasing result of extensively separating salts and/or solids from the raw fluid then intended for further processing.

(7) By way of example, FIG. 2 also shows a chronological sequence of the specific conductivity of a reactant of 10 wt % iso-propanol in water with a salt loading of 0.1 mol/l sodium sulfate and 0.05 mol/l potassium sulfate in a salt separator 2 in accordance with FIG. 1 at a temperature of 450 C. and a pressure of 300 bar. Iso-propanol was consciously selected at this point as it is good at emulating the organic matter of a liquefied biomass slurry which plays a role in the separation of salts. As shown in the figure, the conductivity of the brine increases very rapidly to approximately 30 mS/cm. At the same time, the conductivity of the cleaned raw fluid is close to zero, indicating the complete separation of the sulfates causing the conductivity from the raw fluid.

(8) With regard to the aforementioned European patent application EP 1 772 202 A1, the method for methane production should also be briefly described again: The biomass is conditioned in a 1st procedural step, i.e. crushed and reduced to the desired proportion of dry matter (DM), preferably by means of wet grinding. This results in a pumpable slurry. To improve pumpability, other additives can be added to the biomass (e.g. starch, waste oils). The desired proportion of dry matter is a mass fraction of 5 to 80, preferably a mass fraction of approximately 15 to 40. The method operates particularly economically if the proportion of organic dry matter is a mass fraction of approximately 20 or more. The conditioned biomass slurry is put under high pressure (200-400 bar) in a 2nd procedural step and conveyed continuously or intermittently. Extruders, high pressure eccentric screw pumps, piston diaphragm pumps, and solid material pumps are particularly suitable as conveyors. In a 3rd procedural step the biomass slurry is heated under pressure to 200-350 C. The solid organic biomass components are largely liquefied in the process. For better heating and liquefaction, this process stage may include static mixing elements and/or a catalytic converter (e.g. zinc oxide). In a 4th procedural step the pressurized, heated and liquefied biomass slurry in the salt separator 2 is quickly heated to a higher temperature, preferably in the range of or above the critical temperature of the respective mixture. The critical temperature of water at 374 C. and 221 bar serves as a reference point here. This can take place by means of external heat input (e.g. by means of a burner/catalytic burner which is supplied with recycled product gas) or by adding suitable oxidizing agents (e.g. oxygen, air, hydrogen peroxide, ammonium- and other nitrates) directly in the 4th procedural stage (or one of the preceding process steps 1-3). As a result, most of the salts and remaining solid materials are precipitated and can be collected. The collected precipitates are constantly or periodically removed from the process by way of the second extraction opening 16. The separation and recovery of solid materials as salts in front of the catalytic gasification reactor under hydrothermal conditions and the possible addition of saline oxidizing agents (nitrates, e.g. ammonium nitrate) for partial oxidation of the biomass under hydrothermal conditions improve performance and increase the efficiency of the method substantially. Due to the properties of the source materials, the extracted solid materials are very rich in nitrogen, phosphoric and potassium salts and are therefore particularly suitable for reuse as fertilizers, for example, for agriculture or for algae culture. In a 5th procedural step the hot biofuel (the hot raw fluid), now freed from most of the solid materials, arrives at a reactor fitted with a suitable catalytic converter where gasification to methane, carbon dioxide, hydrogen and traces of carbon monoxide and higher hydrocarbons (ethane, propane) takes place. The catalytic converter preferably comprises ruthenium and in addition may also contain nickel (e.g. Raney nickel) as well as proportions of chrome and/or copper. Other catalytic converters based on Ni, Re, or Rh as the active metal can also be used. The reactor is preferably designed as a fluidized bed reactor, as a monolith reactor or as wall reactor (a tube or tube assembly coated with a catalytic converter). However, tubes could also be used in which catalytically coated sheets of metal are used. In a 6th procedural step the methane-rich product flow is then put to further use. This procedural step can also be used to separate methane from CO2 and the remaining gas components. The product flow can also be cooled to approx. 50 C. and the gas phase separated from the liquid phase under pressure. In a suitable device (e.g. acid scrubbing tower, membrane separation, adsorber) the methane can be separated from the other components from the gas phase and is then available under high pressure (approx. 200 to 400 bar). This results in the omission of a compression step to fill gas cylinders with the methane, to offer it as fuel at a gas service station or to feed it into the gas network. The direct use of the compressed gas as fuel in a gas turbine process is also conceivable.

(9) Hereafter the supply of methane from biomass, among other things for natural gas service stations and/or for feeding into the gas network, for filling in cylinders, or use as fuel in pressure suitable for gas turbines provides strong economic value.

(10) Even if the description of a method for obtaining methane from biomass is paramount here, the salt separator according to the invention can also be used in a method for cleaning other aqueous fluid mixtures. Suitable fluid mixtures are, for example, a pumpable biomass slurry, geothermal effluents, effluent from oil wells and generally, all types of saline process waters, with and without organic matter.